The present invention relates to new and improved thin, soft, absorbent products and more particularly to new and improved soft compressed composites incorporating superabsorbent material and which composites absorb large quantities of liquids.
Disposable absorbent products have been known for some time, including such products as disposable diapers, sanitary napkins, wound dressings, bandages, incontinent pads, and the like. These products incorporate an absorbent batt which is used to absorb and hold or contain body fluids. Initially, in many of these products, especially diapers and sanitary napkins, the absorbent batt comprised what is termed "wadding" or plies of tissue. The wadding was disposed between an impermeable backing and a permeable facing and the plies of tissue were used to absorb and, hopefully, contain the liquid within the product. A diaper which utilizes such an absorbent batt is disclosed in U.S. Pat. No. Re. 26,151.
The wadding type of batt was replaced, for the most part, by an improved absorbent batt which comprises what is termed "fluffed wood pulp fibers". This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. A diaper which incorporates such a fluffed wood pulp absorbent batt is described in U.S. Pat. No. 2,788,003. This diaper had improved absorbent capacity and somewhat better containment than a diaper using a wadding layer. Also the fluffed wood pulp layer is quite soft, flexible and conformable and hence, produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the efficiency with which the capacity is used in a diaper or sanitary napkin is poor. The reason for this, is that the fluid to be absorbed is generally deposited in a localized area within the absorbent batt and the ability for the fluid to move along the plane of the batt is poor. The fluid follows the path of least resistance and consequently moves to the closest edge of the batt where it generally is no longer contained and the product leaks. Furthermore, the wood pulp batts lack stability, e.g., when a diaper is being worn, the batt tends to break up creating bunching.
U.S. Pat. No. 3,017,304 discloses an absorbent product which incorporates in the product a densified, paper-like layer. This paper-like layer acts as a wick, i.e., liquid which is placed on the layer tends to move rapidly along the plane of the layer. When incorporated in combination with fluffed wood pulp fiber, the resultant product uses the absorbent capacity of the fluffed wood pulp much more efficiently. Diapers which incorporate this paperlike layer combined with fuffed wood pulp are disclosed and described in U. S. Pat. Nos. 3,612,055 and 3,938,522. This concept of combining a wicking or capillary skin or layer with fluffed wood pulp fibers has gained wide acceptance in many absorbent products including disposable diapers and sanitary napkins. Even though these products make much greater use of the capacity of the absorbent batt, they still do not totally contain the absorbed liquid. It is probable that these products will leak before the full capacity of the batt is used for absorption. This is especially true if pressure is placed on the batt while wet, for example a baby sitting down on a previously wetted diaper will very often cause the batt to leak. Although the batt is somewhat stabilized by the paper-like densified skin, it may crack and separate.
Recently, elastic leg diapers or stretch diapers have been introduced into the marketplace. Though these diapers provide no better absorbent batt than flat diapers or the prior art diapers, they have indicated improved containment of liquid. Such diapers are disclosed and described in U.S. Pat. Nos. 3,860,003, 4,050,462, and 4,324,245. Though the containment features are better than the prior art products, the elasticized products fit more tightly permitting less air circulation. Frequently, this can become irritating to the skin and the tighter the elastic or the more close fitting the diaper, the greater the irritation. This is especially true adjacent the area where the elastic leg portion of the product contacts the wearer.
A number of years ago "superabsorbent materials", i.e., materials which will absorb many times their weight of liquid, were developed. Since the development of such materials, people have been trying to incorporate them in absorbent products such as diapers and sanitary napkins to enhance the absorptive performance of these products. Theoretically, a minimum amount of superabsorbent incorporated in a product would make that product perform as well or better than the prior art products. Perhaps one of the first products to incorporate such a superabsorbent material in a disposable diaper is disclosed in U.S. Pat. No. 3,670,731. This patent discloses an absorbent dressing comprising an absorbent layer sandwiched between a permeable facing and an impermeable backing sheet. The absorbent layer contains water insoluble cross-linked hydrocolloid polymer as the superabsorbent material.
Even though superabsorbent materials have been available for some time, they have not gained wide acceptance in absorbent products such as disposable diapers and sanitary napkins. A primary reason for this lack of acceptance of the superabsorbents is failure to develop a product capable of economically utilizing the highly increased absorptive capacity of the superabsorbent materal. In order to economically utilize a superabsorbent, the liquid being absorbed must be transported to the superabsorbent material. In other words, the superabsorbent material must be placed in contact with the liquid. Furthermore, as the superabsorbent material absorbs the liquid, it must be allowed to swell. If the superabsorbent is prevented from swelling, it will cease absorbing liquid. Hence if the superabsorbent material is to function in diapers and sanitary napkins wherein the liquid to be absorbed is placed in a small void area, the structure of the absorbent layer containing superabsorbent materials appears to be critical. Over the years a number of techniques have been disclosed in an attempt to provide structures which make efficient use of the superabsorbent material. Such products are disclosed in U.S. Pat. Nos. 4,103,062, 4,102,340, and 4,235,237. In addition, methods for incorporating superabsorbents into suitable layers or suitable configurations which can be placed in an absorbent product, are disclosed in U.S. Pat. Nos. 4,186,165, 4,340,057 and 4,364,992. To date, none of these products has met with any substantial commercial success.
In copending appplication Ser. No. 439,963 filed Nov. 8, 1982, a particularly useful compressed composite is formed. This application is hereby incorporated by reference. The compressed composite product is preferably made from a nonwoven fabric such as polyester. The fabric has associated with it at least 200 percent by weight of superabsorbent to form an absorbing layer. In order to provided a product which will not only absorb liquid but also transport liquid, wood pulp fibers or other suitable wicking materials are cast in a layer on at least one side of the absorbing layer. The product is then compressed to yield a very high liquid absorbing product. However, the resulting compressed composite is quite stiff, and hence requires softening to provide flexibility for utilization in products such as diapers and the like. The flexibility provided needs to be permanent, i.e. the surrounding environment, handling of the product and its subsequent use will not affect the softness and flexibility.
The present invention provides a new and improved absorbent composite structure which utilizes a substantial portion of the absorptive capacity of superabsorbent materials and yet is soft and flexible. This soft, flexible composite is substantially completely stable and retains its stable state even though rendered soft and flexible. Whether wet or dry the composite does not break, bunch or separate. The soft composite retains absorbed liquid without yielding any of the liquid when the composite is under pressure.